1. Field of the Invention
This invention relates generally to fuel cells for providing portable electricity. More specifically, this invention relates to miniature solid oxide fuel cells which are employed to provide power, typically in the form of direct current electricity, to portable devices such as cellular phones, notebook computer, and medical devices.
2. Background Art
A commonly employed method for providing electricity to portable devices is to utilize a battery or batteries. Batteries are used in a range of devices from flashlights to cellular phones. Batteries may be single use or rechargeable. Problems such as discharge have led to attempts to develop replaceable power sources which would utilize a fuel to create electricity.
Single use batteries are probably the most commonly used battery today. Single use batteries employ a dry cell or series of dry cells. Typically each cell produces 1.5 volts. The cells are connected in series to achieve the desired voltage. The associated current, and thus the total electrical energy available, is dependent on the size of the cell.
A typical dry cell well known in the art would employ a zinc coated metal container which would enclose all of the chemical ingredients and which would also serve as the negative electrode. The positive electrode would consist of a carbon rod. A paste of ammonium chloride, zinc chloride, and water would serve as the electrolyte.
The positive terminal or anode of such a cell would be surrounded with a thin layer of powdered carbon and manganese dioxide. When a load is place across the anode and the negative terminal or cathode, ammonium ions gain electrons at the carbon rod and zinc ions are formed at the cathode. This process results in the formation of ammonia gas and hydrogen.
A chemical reaction takes place between the ammonia gas and the zinc chloride. Additionally, the hydrogen and the manganese dioxide chemically react. These reactions result in the output of electricity.
Eventually, the chemical components necessary to produce electricity are depleted and the cell is no longer usable. A battery comprised of dry cells is discarded at this point.
Another type of battery utilizes what are often referred to as wet cells. Lead acid batteries are well known in the art and fit into this general category. In this type of battery, it is possible to reinitialize or recharge the battery upon discharge.
Some rechargeable batteries also exhibit another undesirable characteristic known as memory. Memory is a term used to describe the effect seen when a rechargeable battery is charged prior to becoming fully discharged. Batteries susceptible to this effect will remember to what level they had discharged and will only provide power to that level, even though power should be available below that level. This effect can cause a battery which should have a life of several hours to be reduced to an effective life of less than an hour per recharge. This is a highly undesirable effect which can severely curtail the usefulness of a rechargeable battery.
The disadvantage of discharge is exhibited by batteries using both dry cells and wet cells. Although some progress has been made in terms of battery life, charging time, and shelf life, nevertheless most batteries will eventually be discarded. Single use batteries are discarded when they become discharged. Rechargeable batteries have an advantage over disposable batteries in that they can be recharged and used again. The number of times a rechargeable battery may be discharged and recharged is typically limited, however, and eventually even rechargeable batteries will require disposal.
The disadvantages and limitation of supplying power via batteries, particularly with regard to large applications has lead to attempts to develop alternative portable power supplies. One such alternative is the ceramic fuel cell. Ceramic fuel cells utilize an electrochemical combustion of hydrogen to produce direct current electricity. The hydrogen is typically derived from a hydrocarbon fuel, alcohol, or coal. Ceramic fuel cells are also commonly known as solid oxide fuel cells due to the predominant use of oxides as the electrolyte.
Solid oxide fuel cells have enjoyed some success, however they are also possessed of a number of characteristics which make them unsuitable to provide portable power to devices such as cellular phones, notebook computers, and medical instruments. For example, prior art solid oxide fuel cells are typically large and somewhat cumbersome. The large size of the typical prior art solid oxide fuel cell does not lend itself to use in small devices.
In addition, the high operating temperatures at which solid oxide fuel cells operate make them seemingly unsuitable for incorporation in hand held devices. Further, the time interval required for a solid oxide fuel cell to begin producing direct current electricity is on the order of hours. Clearly such a lengthy start up time is annoying at best in use with devices designed for convenience such as cellular phones and notebook computers. Further, such a lengthy start up time prohibits the use of solid oxide cells in medical devices which may be instantly required for use in medical emergencies.
It would, therefore, be an advantage in the art to provide a ceramic fuel cell which would be adapted for incorporation in small, often hand held, portable devices and, accordingly, which would exhibit the characteristics of quick start up and heat management.